Two weeks of rain, and the cover crop still has to go into the ground. What driving on it really costs, which options remain — and where seeding from the air reaches its limits.
The pattern repeats every year, only the date shifts: the harvest is done, the seed is in the store, the drill is ready — and then it rains for ten days. Afterwards the farm manager stands at the edge of the field, steps into the combine's wheel track and knows it is not a good idea. Only: the calendar does not wait, and a cover crop seeded at the end of September is a different stand from one seeded in mid-August.
That is precisely the dilemma. There is no method that resolves it, but there are several ways out — and they come at different prices. This article sorts them: what driving on wet soil actually does, which four options the farm has left and where seeding from the air really helps. Including the cases in which it does not.
The discussion usually only covers the first, although the second is often the more expensive one.
A moist soil is plastic. It no longer springs back but deforms permanently — the pores through which water drains and air reaches the roots are squeezed shut. At the top, in the topsoil, the farm recovers this over time through tillage, frost and rooting. Further down, in the subsoil, it does not: what is compacted there is out of reach of tillage and stays for years. And the depth to which compaction reaches depends less on tyre pressure than on axle load — the heavier the machine, the deeper it acts.
The consequences are unspectacular and therefore easy to overlook: poorer water infiltration, more surface runoff and erosion, stunted root growth, less usable soil water in the next dry summer. You do not see them on the day of the pass, but two crops later.
A cover crop builds biomass through heat sum and day length, and both decline daily from midsummer onwards. That is why the loss from waiting is not linear: two weeks of rain in August cost disproportionately more growth than two weeks in July. Anyone who waits until the soil carries often seeds into a window in which seeding barely pays off agronomically any more — and then pays for seed and operation to get a stand that never makes it past ten centimetres. The details are in the article Seeding cover crops.
The honest field test of whether your soil will carry. Take a handful from the topsoil and roll it between your palms. If it can be rolled into a shiny sausage without breaking, the soil is past the point at which it behaves elastically — every pass then deforms it permanently. Second test: drive a short stretch and look back. If the track stays put and the soil sticks to the tyres instead of falling off, you have your answer. Neither replaces a soil analysis, but both are more honest than a glance at the weather forecast.
If the soil will not carry, the farm realistically has four ways forward. None of them is free; the difference lies in where the costs land.
| Option | What it costs | When it is right |
|---|---|---|
| Wait until it dries off | Growing season — and the risk that the next front arrives faster than the drying | Early in the season, when there are still weeks of buffer in the calendar |
| Drive anyway | Soil structure, permanently in the subsoil; plus wheel slip, diesel and a poorer seedbed | Almost never the deliberately right choice — usually the decision you make because no other seems left |
| Drive lighter (tyre pressure control, dual wheels, smaller rigs) |
Investment or setup time; mainly reduces the load on the upper layers | Sensible as a permanent solution on the farm — but no longer helps once the soil will not carry anyway |
| Seed from the air | The service, a surcharge on the seed and the missing seed-to-soil contact | When the window is open now and the soil does not allow it |
The third option is underrated and is often the most effective for day-to-day operations — but it solves a different problem. Tyre pressure decides the load on the topsoil, axle load decides the depth effect. On a soil that already deforms under a footprint, driving lighter only shifts the limit, it does not remove it.
The decisive point is not that a drone is modern. It is that it separates two things that are coupled in every ground-based method: the question of whether seeding is possible, and the question of whether driving is possible.
For germination, a moist soil is not a problem but the ideal case. The real risk of broadcast seeding without seed-to-soil contact is precisely that the seed lies on a dry surface and does not germinate — which is why we otherwise schedule drone seeding to take place shortly before a period of rainfall. On soaked soil this risk disappears completely. The condition that stops the seed drill is the most favourable one there is for seeding from the air.
Add to that the points that weigh more heavily in wet conditions than usual:
The strongest answer to wet conditions is not a method for the wet field but one that does not wait for the wet field at all: pre-harvest seeding into the standing crop. The seed is applied one to three weeks before harvest over the ripening main crop, falls to the ground and lies there in the shade of the crop — protected, with good residual moisture. The combine drives over it, the chopped straw covers it, and the cover crop starts the moment it gets light.
For the question of wet conditions this means two things. First, the seeding is already done before the question of trafficability even arises. Second, there is almost always moisture under a standing crop — so the method is not only suitable for wet conditions, it depends on moisture and finds it more reliably there than on open stubble. The same principle underlies undersowing into the standing crop, where the main crop would otherwise be driven down.
The catch is an organisational one: the window is before the harvest, not after. Anyone who calls when the combine has already left the field can no longer choose pre-harvest seeding for this year — what remains is seeding onto the stubble, which also works but no longer gives the two to three weeks' head start.
We fly drone seeding as a contractor, and still: there are cases in which we will tell you it does not fit. The limits are known and can be planned for — they just cannot be argued away.
Fine to medium seeds fly very well: mustard, oil radish, Phacelia, niger, clover-grass and ryegrass. Vetches and small peas also work. Coarse, heavy seed such as field bean or large lupin belongs in the drill — wet conditions do not change that, they only make it more annoying. And the higher the application rate per hectare, the more flight time and reloading are required; at very high rates the calculation tips back in favour of ground-based machinery. The guide values for the common species are in the table in the article Seeding cover crops.
Wind is the most common reason a date does not hold. It distributes fine seed unevenly, and at the edges the delineation becomes untidy — with Phacelia sooner than with oil radish. Above the limits set by the manufacturer's specifications and the operating approval we do not fly, and that is not negotiable. In practice this means: early in the morning or in the evening when it is calm, and a calendar that can tolerate a shift of one day.
In ongoing rain, with a risk of thunderstorms or in poor visibility nobody flies — this is also in our terms and conditions, because it regularly leads to rescheduling. But the difference from driving is exactly the one this article is about: we do not need a dried-off field, only a dry window in the air. A few hours between two fronts are enough. The soil may stay soaked — and the wetter it is, the better for emergence.
The most honest disadvantage last. Drone seeding is broadcast seeding onto the surface; it lacks the defined placement depth of the drill. Field emergence therefore depends on surface moisture: on dew, on the night hours in which the surface takes up water again, on straw or crop as cover. In wet conditions this is the most favourable case — nevertheless we allow for a surcharge of around 10 to 20 percent on the seed rate compared with drilling. That is not a disadvantage of the drone but of the method, and it can be budgeted for.
As soon as the soil carries again, a pass with the roller or a shallow straw harrow lifts emergence noticeably — with seeding onto the stubble that is the ideal case. With pre-harvest seeding into the standing crop it is not needed; there, residual moisture and chopped straw take over. Two more things belong here for completeness: in persistently wet weather, slug pressure on seed lying on the surface is higher than in dry weather, and nothing germinates in standing water — hollows in which water stands for days are not worth seeding from the air either.
Wet-weather jobs are short-notice jobs. The difference between "this week" and "next week" almost always comes down to preparation, not the weather.
There is no fixed figure — load-bearing capacity depends on soil type, structure, humus content, previous loading and above all on the current water content. In practice you test it in the field: if the soil can be rolled into a shiny sausage, sticks to the tyres and the track stays put instead of springing back, the limit has been exceeded. Heavy soils reach it sooner after rain and leave it later than light ones.
The soil is rarely the problem; the machine on top of it is. A moist surface is actually ideal for germination. From the air, the two can be separated: seed onto a receptive soil without anything driving over it.
Not in ongoing rain, with a risk of thunderstorms, in too much wind or in poor visibility. But it does not need a dried-off field, only a dry window in the air — a few hours between two fronts are enough.
Fine to medium seeds: mustard, oil radish, Phacelia, niger, clover-grass, ryegrass, also vetches and small peas. Field bean and large lupin belong in the drill. Very high application rates per hectare drive up flight time and thus costs.
Exactly the same as on a trafficable one — the condition of the soil changes nothing, because the drone does not touch it. The price is determined by area and shape, application rate, travel distance and the question of material. In the order portal you see the guide price for your field in about two minutes.
Wet soil forces a choice between two losses: structure or growing season. Seeding from the air is the way not to have to make that choice — with a seed surcharge and no seed-to-soil contact as the price. It is strongest when you plan it before the rain comes: as pre-harvest seeding into the standing crop. What we specifically offer is on the service pages Seeding cover crops by drone, Undersowing by drone and Fertilization by drone — the latter in case it is not the seeding but the foliar fertilization that depends on trafficability.
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